In many applications there is a requirement for inexpensive transparent conducting layers, but a busbar will be also required for some of the (large area) applications. Highly conductive (non-transparent) patterns can be made by screen-printing conducting pastes such as silver or carbon black pastes. Vacuum evaporation of metals through shadow masks is another method. Yet another method makes use of homogeneous conductive metallized surfaces which can be patterned by use of photoresist technology in combination with a metal etching agent. Photographic films can, under certain conditions, be used for making electrically conductive silver “images”.
U.S. Pat. No. 3,664,837 describes the use of light sensitive evaporated silver halide film which upon exposure and after development results in conductive images. DE 1,938,373 describes a photographic method for producing conducting paths, resistances and capacitors for microcircuits starting from coated silver halide emulsions. U.S. Pat. No. 3,600,185 describes the production of electrically conductive patterns by means of diffusion transfer techniques.
Combinations of a transparent polymer-based conductor and a high conductive (non-transparent) pattern are described in some publications. DE-A 196 27 071 discloses an electroluminescent configuration, which contains hole and/or electron injecting layers, wherein the polymeric organic conductor is selected from the group of polyfurans, polypyrroles, polyanilines, polythiophenes and polypyridines. DE-A 196 27 071 also discloses the use of poly(3,4-ethylenedioxythiophene) as a charge-injection layer on transparent metallic electrodes such as ITO (indium-tin oxide) and that the following materials are suitable as transparent and conductive materials: a) metal oxides e.g. ITO, tin oxide etc.; b) semi-transparent metal films e.g. Au, Pt, Ag, Cu etc. The latter being applied by vacuum techniques.
EP-A 510 541 discloses an organic electroluminescent device having an anode, an organic hole injection transport layer, an organic luminescent layer and a cathode formed sequentially in this order, wherein the organic hole injection transport layer contains a metal complex and/or a metal salt of an aromatic carboxylic acid. EP-A 510 541 further discloses that the conductive layers used in such devices may have a multi-layer structure by depositing different types of conductive materials selected from a metal, e.g. Al, Au, Ag, Ni, Pd or Te, a metal oxide, carbon black or a conductive resin such as poly(3-methylthiophene), but no specific combinations are exemplified.
U.S. Pat. No. 5,447,824 discloses a method of manufacturing a pattern of an electrically conductive polymer on a substrate surface, said method comprising: a) forming a liquid layer on a surface of said substrate from a solution containing a material capable of forming said electrically conductive polymer upon being heated, e.g. 3,4-ethylenedioxythiophene, an oxidizing agent and a base, b) exposing said liquid layer to patterned radiation, and c) heating said layer thereby forming a pattern of an electrically conductive polymer, said conductive polymer being formed in unexposed areas and a non-conductive polymer being formed in the exposed areas of the layer. The galvanic provision of the conductive polymer pattern with a metal layer, e.g. silver, copper, nickel or chromium, is also disclosed in U.S. Pat. No. 5,447,824.
U.S. Pat. No. 5,973,050 discloses a conductive composition of matter comprising a dispersion of nanophase metal particles in an intrinsically conducting polymer with nanophase metal particles being preferably selected from the group consisting of silver, copper, platinum, palladium, aluminum, chromium, iron, antimony, tin, tantalum, gold, similar metals and mixtures thereof, and the intrinsically being preferably a conjugated polymer e.g. polythiophene, polyaniline, polypyrrole, polyacetylene, their substituted derivatives and similar polymers.
U.S. Pat. No. 5,919,402 discloses a composition, comprising: (a) a three dimensional matrix formed by photopolymerizing an electronically conducting polymer; and (b) silver grains substantially uniformly distributed throughout the matrix and having a diameter less than about 5 μm.
U.S. Pat. No. 6,015,509 discloses a composition comprising a thermoset or thermoplastic polymeric matrix, and a conductive filler component, where said filler component comprises electrically conductive particles and at least one conducting polymer selected from the group consisting of substituted and unsubstituted polyparaphenylenevinylenes, substituted and unsubstituted polyanilines, substituted and unsubstituted polyazines, substituted and unsubstituted polythiophenes, substituted and unsubstituted polyparaphenylenes, substituted and unsubstituted poly-p-phenylene sulfides, substituted and unsubstituted polyfuranes, substituted and unsubstituted polypyrroles, substituted and unsubstituted polyselenophenes, substituted and unsubstituted polyacetylenes, mixtures thereof, and copolymers thereof, being obtained by separately admixing the conducting polymer and the conductive is particles with the polymeric matrix.
WO 98/54767 discloses a conductive layer system, particularly for a transparent or semi-transparent electrode or electroluminescent configuration, comprising at least two layers, characterized in that the first layer contains an organic or organometallic electrically conductive polymer, which is transparent or semi-transparent in the visible range of the electromagnetic spectrum, e.g. a polymer selected from the group consisting of polythiophene, polypyrrole, polyaniline, polyacetylene or their optionally substituted derivatives and the second layer contains at least one electrically conductive inorganic compound or a metal or an appropriately doped semi-metal e.g. a material selected from the group consisting of Cu, Ag, Au, Pt, Pd, Fe, Cr, Sn, Al or their alloys or conductive carbon. In a preferred embodiment the second layer is a conductive pattern formed by an open grid structure, preferably with a 5–500 μm grid so that it cannot be perceived by the human eye. Invention example 2 discloses a poly(3,4-ethylenedioxythiophene) [PEDOT]/poly(styrene sulphonate) [PSS] layer with a surface resistivity of 1500 Ω/square to which conducting tracks of Leitsilber™ (a silver particle dispersion) ca. 2 mm wide had been applied by a printing technique.
The layer configuration disclosed in Example 2 of WO 98/54767 has the disadvantages of the grid of Leitsilber™ requiring a thickness of 5 to 10 μm to realize layers with a surface resistance of 0.5 to 1 Ω/square, which means that the surface of the configuration will have a certain roughness which will limit its applications, making it difficult to apply a thin, e.g. 100 nm, functional layer. Furthermore, an aqueous PEDOT/PSS dispersion would not wet such a Leitsilber™ grid and hence a usable multilayer conductive configuration would not result.
Moreover, with an intrinsically conductive polymer layer or a metal grid outermost wetting problems arise as regards coating of thin functional layers. Furthermore, for devices requiring very thin functional layers such as transistors, the thickness of a multilayer electrode and even slight deviations from flatness are disadvantageous in their production.